The primary energy requirements of the normal myocardium are met by the oxidation of long-chain fatty acids. Radiolabeled long-chain fatty acids presently used clinically for myocardial imaging include 11C-palmitic acid and various w-radioiodinated fatty acids. The use of these fatty acids for myocardial imaging presents several distinct limitations which include rapid metabolism and wash-out of the radioactivity from the myocardium. In the case of the radioiodinated fatty acids, high blood levels of radioactivity present an additional problem. The identification of structural features which will increase the myocardial residence time but not decrease the heart uptake of long-chain fatty acids is therfore of interest. Several unique long-chain fatty acids labeled with Te-123m show pronounced and prolonged heart uptake in laboratory animals. Furthermore, myocardial imaging has been demonstrated in rats, rabbits and dogs with the Te-123m-labeled fatty acids. These agents also show rapid heart uptake and the blood levels of radioactivity decline very rapidly. Preliminary results suggest that the uptake and retention of these unusual fatty acids represents a new type of metabolic trapping. We propose to develop rapid synthetic techniques using organoborane reagents for the introduction of terminal halogens into long-chain fatty acids containing stable tellurium. The presence of the tellurium heteroatom represents a structural perturbation which will result in the prolonged retention of the radiohalogenated fatty acids in the heart tissue. In addition, we will develop rapid synthetic techniques for the introduction of radiocarbon into the tellurium fatty acids. Iodinated and brominated Te-123m-labeled fatty acids will be prepared and tested in rats. Agents identified in these preliminary studies will then be radiohalogenated and tested further in rats. Successful candidates will be tested in a variety of animal species and the results of these extensive biological studies will be used to extrapolate the absorbed radiation dose values to humans to assess the potential clinical usefulness of these new myocardial imaging agents.